1. Field of the Invention
This invention relates generally to an improved tire tread applicable for retreading a worn tire carcass and, more particularly, to an improved tire tread for retreading a worn tire carcass that includes uncured wing portions that are cross-linked to the side walls of the tire carcass so as to provide a smooth transition between the tire side walls and the tread.
2. Discussion of the Related Art
As is well understood in the art, it is highly desirable to apply a new tire tread to worn rubber tires for all types of vehicles using such tires. When the original tread of a rubber tire has been worn from use and/or has deteriorated from exposure to environmental conditions to such a degree that the tire has significantly reduced traction capabilities, and thus is no longer safe for continued use, the used tire carcass can be conditioned to accept a new tire tread so as to revitalize the old tire to make the original tire safe to be used again. By retreading used tire carcasses, the tire carcass need not be discarded and as such environmental concerns directed to the disposal of old tires can be positively addressed. Further, less rubber resources are necessary to generate a piece of tire tread, as opposed to a whole new tire. Also, providing a retreaded tire is less costly than a new tire.
Two types of retread processes are the most common in the art. A first type of retread process is referred to as a mold cure process. In the mold cure retread process, the remaining tread of a worn tire carcass is ground off so as to generate a suitable roughened surface to accept a new tire tread. The tire carcass is then placed in a tire mold that is similar to the tire mold that would have been used to mold the original tire. Uncured tread rubber is then placed into the mold, and the mold is pressurized and heated such that the tread rubber is vulcanized or cured into a tread pattern and cross-linked to the tire carcass. Once the mold is cooled, a retreaded tire is produced that resembles the original tire.
The mold cure process is a successful tire retreading process. However, the mold cure retread process requires tire molds that are expensive. Because of this sizable investment, it has been known in the art to retread worn tire carcasses by what is referred to as a precure retreading process. U.S. Pat. No. 4,624,732 issued to King, herein incorporated by reference, discloses a known precure retreading process. As with the mold cure process, the remaining tread and side walls of a worn tire carcass are ground down to form a roughened surface applicable to accept a new tread and side walls. A premolded and precured tire tread is then provided that will be adhered to the prepared tire carcass. An uncured rubber bonding layer is applied to the tire carcass, and the precured tire tread is then wrapped around the tire carcass over the bonding layer. The tire carcass and precure tread are secured together within an envelope to form a retread tire assembly. The retread tire assembly is then placed in an oven or autoclave, and is heated under pressure such that the bonding compound layer is cured so as to cause a cross-linked bond between the tread and the tire carcass. As is apparent by studying the precure process, entire tire molds are not necessary in that the tire tread is already molded and cured prior to being applied to the tire carcass.
An extension to the precure retread process discussed above includes providing new side walls to a tire carcass that also have been deteriorated by wear. U.S. Pat. No. 4,869,759, issued to King et al and herein incorporated by reference, discloses a method and apparatus for replacing a side wall of a worn tire carcass that can be used in conjunction with the precure retreading process discussed above. The side wall replacement process includes inserting uncured rubber panels within the envelope that conform to the shape of the tire carcass side wall. Once the tire assembly is placed in the autoclave, the side wall panels are cured and cross-linked to the side wall of the tire carcass in the same manner as the tire tread.
FIG. 1 shows a cross-sectional view of a prior art precured tread 10 before it is secured to a tire carcass (not shown) in a precure retread process. The tread 10 includes a top surface 12 through which a tire tread pattern 14 has been formed by a precure molding process. The tire tread 10 also includes a bottom surface 16 that will be positioned in contact with a rubber bonding layer that has been applied to the tire carcass when the tread 10 is to be secured to the tire carcass, as discussed above. The tire tread 10 also includes shoulders 18 and 20 that are angled towards each other from the bottom surface 16 to the top surface 12 as shown. After the tread 10 is molded and cured, excess flash rubber is trimmed along the bottom edges of the shoulders 18 and 20 of the tread 10 forming ridges 22 and 24, respectively. When the tire tread 10 is attached to the tire carcass, the shoulders 18 and 20 continue into the side walls of the tire carcass.
Because the tire retread is precured prior to being attached to the tire carcass, there generally exists a noticeable transition point where the tread shoulders meet the side wall of the tire carcass. In other words, there is a lack of continuation between the tire side wall and the tread shoulder that leaves a band appearance. Additionally, because of the significant transition between the tire carcass side wall and the tire tread, there also exists an inherent weakness for separation of the tread from the tire during use of the retreaded tire, thus generating at least somewhat of a safety concern.
In order to alleviate the above concerns, it has heretofore been known in the art to provide winged portions that extend from the bottom edges of the shoulders of a precure tire tread in order to increase the bonding ability of the tread to the tire carcass, as well as reduce the transition of the tread to the sidewalls of the tire carcass. FIG. 2 shows a cross-sectional view of a prior art winged tread 30. The winged tread 30 also includes a top surface 32 having a tread pattern 34 opposite to a bottom surface 36 that will be formed to a tire carcass in the manner as discussed above. The winged tread 30 also includes angled shoulders 38 and 40. Wing portions 42 and 44 extend from the bottom edges of the shoulders 38 and 40, respectively, so as to cause an extension of the bottom surface 36 of the tread 30, as shown; When the tread 30 is wrapped around the tire carcass, the wing portions 42 and 44 will extend partially down the side walls of the tire carcass, and thus lessen the noticeable transition between the tread 30 and the tire carcass sidewalls when the tread 30 and the tire carcass are bonded together.
Another prior art precure tire tread having wing portions is shown by a cross-sectional view in FIG. 3. This figure shows a gold wing tread 50 that includes a top surface 52 having a tread pattern 54, and a bottom surface 56 to be formed to a tire carcass. The tread 50 also includes wing portions 58 and 60 that extend from angled shoulders 62 and 64, respectively, of the gold wing tread 50. The wing portions 58 and 60 of the tread 50 offer a different type of continuity from the tread 50 to the tire carcass side wall than the tread 30 above.
Although the treads 30 and 50 have been successful in reducing the transition between the side wall of the tire carcass and the tread in the precure process, as well as increasing the ability of the tread to be better secured to the tire carcass, there still remains improvement in this area. Consequently, it is is an object of the present invention to provide a precure tire tread and method of applying the tire tread to a tire carcass in which winged portions extending from the sides of the tread lessen the transition between the retread and the side walls of the tire carcass.